Description of the Related Art
Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of a person""s oxygen supply. Early detection of low blood oxygen level is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. A pulse oximetry system includes a sensor applied to a patient, a pulse oximeter, and a patient cable connecting the sensor and the pulse oximeter. The pulse oximeter may be a standalone device or may be incorporated as a module or built-in portion of a multiparameter patient monitoring system and typically provides a numerical readout of the patient""s oxygen saturation, a numerical readout of pulse rate, and an audible indicator or xe2x80x9cbeepxe2x80x9d that occurs in response to each pulse. In addition, the pulse oximeter may display the patient""s plethysmograph, which provides a visual display of the patient""s pulse contour and pulse rate.
FIGS. 1 and 2 illustrate one type of circuit configuration for a pulse oximetry sensor, such as described in U.S. Pat. No. 5,782,757 entitled xe2x80x9cLow Noise Optical Probe,xe2x80x9d which is assigned to the assignee of the present application, and is incorporated herein by reference. As shown in FIG. 1, a sensor 100 that can be attached, for example, to an adult patient""s finger or an infant patient""s foot, has both red and infrared LEDs 110 and a photodiode detector 120. For finger attachment, the sensor is configured so that the LEDs 110 project light through the fingernail and into the blood vessels and capillaries underneath. The photodiode 120 is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues. The sensor 100 may have an identification (ID) element, such as a resistor 130 with multiple uses depending on the manufacturer, such as an indicator of LED wavelength, sensor type or manufacturer. LED pinouts 140 connect the LEDs 110 to LED drivers in a pulse oximetry monitor (not shown) via a patient cable (not shown). Detector pinouts 150 connect the detector 120 to front end signal conditioning and analog-to-digital conversion within the monitor, also via the patient cable.
As shown in FIG. 2, a sensor circuit may comprise a flexible circuit substrate 200 having printed traces 204 of deposited or etched conductive material, including connector traces 206. Mounted on the substrate 200 and soldered to the traces 204 so as to create an electrical connection are an LED component 210 having both red and infrared LEDs 110 (FIG. 1) encapsulated on a leaded carrier, a detector component 220 having a photodiode 120 (FIG. 1) encapsulated on a leaded carrier and an ID element 230 such as a resistor 130 (FIG. 1) on a leadless carrier. The connector traces 206 have detector pinouts 140, LED pinouts 150 and shielding pinouts 260 for noise suppression.
A ribbon cable substrate pulse oximetry sensor utilizes a ribbon cable to physically mount and electrically connect the sensor components. A ribbon cable substrate has several advantages over a flexible circuit or similar substrate for manufacturing a pulse oximetry sensor. Ribbon cable can be purchased xe2x80x9coff-the-shelfxe2x80x9d in bulk quantities, such as on large spools, as compared with flexible circuits, which are custom manufactured. Further, unlike flexible circuits that must be manufactured in various sizes for various sensor types, ribbon cable can be cut-to-length as required. In additional, as described below, ribbon cable is amenable to automated manufacturing techniques. Thus, use of ribbon cable as a sensor substrate can significantly reduce sensor costs as well as simplify the manufacturing process.
One aspect of a physiological sensor comprises a ribbon cable having a plurality of conductors extending within an insulation layer between a first end and a second end. A detector is mounted to the ribbon cable and electrically connected to at least a first pair of the conductors. An emitter is also mounted to the ribbon cable and electrically connected to at least a second pair of the conductors. At least one of the detector and the emitter are mounted at the first end of the ribbon cable, and a connector is mounted to the ribbon cable at the second end. A retainer is mounted to the ribbon cable and configured to removably attach the ribbon cable to tissue so that the emitter may transmit light into a tissue sample and the detector may receive light from the tissue sample.
In one embodiment, the detector is mounted to the ribbon cable at the first end and the emitter is mounted to the ribbon cable between the first and second ends. In this manner, the ribbon cable can be folded around a tissue portion of a patient so that the emitter opposes the detector on either side of the tissue portion. In another embodiment, the connector comprises a plurality of pins each enclosing one of a plurality of end portions of the conductors, where the insulation is stripped from the end portions at the second end. An encapsulant is disposed around a portion of the pins and the second end so as to form a housing portion of the connector. Alternatively, a welded connector shell is disposed around a portion of the pins and the second end so as to form a housing portion of the connector.
In a further embodiment, the ribbon cable comprises a first conductive layer shielding the first pair of conductors, where the first conductive layer has a first embedded conductor extending to the connector. A detector shield may be disposed around the detector and electrically connected to the first embedded conductor. Also, there may be a second conductive layer shielding the first pair and the second pair of conductors, where the second conductive layer has a second embedded conductor extending to the connector.
Another aspect of a physiological sensor is a manufacturing method comprising the step of cutting a substrate from a length of ribbon cable having a plurality of conductors to form a connector end and a component end of the substrate. The length of the substrate is measured to conform to a particular sensor type. Further steps are stripping a first portion of insulation from the component end to expose a detector contact portion of the conductors and stripping a second portion of insulation from the component end to expose an emitter contact portion of the conductors. Additional steps are attaching a detector and an emitter at the component end so that a plurality of detector leads of the detector are electrically connected to the detector contact portion and a plurality of emitter leads of the emitter are electrically connected to the emitter contact portion. Additional steps are forming a connector at the connector end configured to electrically communicate with a patient cable and mounting the substrate to a retainer configured so that the substrate can be attached to living tissue. In one embodiment the attaching step comprises the substep of crimping the detector leads and the emitter leads onto the detector contact portion and the emitter contact portion, respectively.
In one embodiment, the forming step comprises the substeps of stripping a third portion of insulation from the connector end to expose a connector contact portion of the conductors, disposing a plurality of pins around the connector contact portion, and encapsulating the pins to form a connector housing. In an alternative embodiment, a substep is welding a connector shell around the pins to form a connector housing. The connector contact portion is in electrical communication with the detector contact portion and the emitter contact portion. Another embodiment comprises the further steps of removing an insulation window between the connector end and the component end to expose an ID element contact portion of the conductors, and attaching an ID element within the window so that a plurality of ID element leads of the ID element are electrically connected to the ID element contact portion. Yet another embodiment comprises the further steps of exposing a detector shield conductor at the component end, where the detector shield conductor is embedded within a conductive layer of the substrate extending from the component end to the connector end, attaching a shield to the detector, and electrically connecting the detector shield conductor to the detector shield.
Yet another aspect of a physiological sensor comprises an emitter means for transmitting light into tissue, a detector means for receiving light from tissue, a connector means for providing external instrument communication, a ribbon cable means for conducting electrical signals between the connector and each of the emitter and the detector, and a retainer means for attaching the ribbon cable means to tissue. In one embodiment, the physiological sensor further comprising a window means for attaching an ID element to the ribbon cable means. In another embodiment, the physiological sensor further comprises a first shielding means disposed within the ribbon cable means for suppressing electrical noise at the detector. A second shielding means may also be disposed within the ribbon cable means and around the first shielding means for suppressing electrical noise.